Method for electricity measurement for v2v communications in wireless communication system, and device for same

ABSTRACT

The present invention relates to a method for electricity measurement by a vehicle-to-vehicle (V2V) device for V2V communications in a wireless communication system and to a device therefor. In particular, the present invention comprises the steps of: receiving at least one synchronization signal for V2V through a physical sidelink broadcast channel (PSBCH); and measuring received electricity from said at least one synchronization signal if the ID of said at least one synchronization signal is linked to a demodulation reference signal (DMRS) sequence having, applied thereto, an orthogonal cover code (OCC) having one fixed value, wherein the measurement is performed by means of averaging for each ID of said at least one synchronization signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2016/013085, filed on Nov. 14, 2016,which claims the benefit of U.S. Provisional Applications No.62/254,715, filed on Nov. 13, 2015, 62/291,576, filed on Feb. 5, 2016and 62/374,706, filed on Aug. 12, 2016, the contents of which are allhereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method of measuring power for vehicle-to-vehicle(V2V) communication in a wireless communication system and device forthe same.

BACKGROUND ART

A 3rd generation partnership project long term evolution (3GPP LTE)(hereinafter, referred to as ‘LTE’) communication system which is anexample of a wireless communication system to which the presentinvention can be applied will be described in brief.

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS) which is an exampleof a wireless communication system. The E-UMTS is an evolved version ofthe conventional UMTS, and its basic standardization is in progressunder the 3rd Generation Partnership Project (3GPP). The E-UMTS may bereferred to as a Long Term Evolution (LTE) system. Details of thetechnical specifications of the UMTS and E-UMTS may be understood withreference to Release 7 and Release 8 of “3rd Generation PartnershipProject; Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), basestations (eNode B; eNB), and an Access Gateway (AG) which is located atan end of a network (E-UTRAN) and connected to an external network. Thebase stations may simultaneously transmit multiple data streams for abroadcast service, a multicast service and/or a unicast service.

One or more cells exist for one base station. One cell is set to one ofbandwidths of 1.44, 3, 5, 10, 15 and 20 MHz to provide a downlink oruplink transport service to several user equipments. Different cells maybe set to provide different bandwidths. Also, one base station controlsdata transmission and reception for a plurality of user equipments. Thebase station transmits downlink (DL) scheduling information of downlinkdata to the corresponding user equipment to notify the correspondinguser equipment of time and frequency domains to which data will betransmitted and information related to encoding, data size, and hybridautomatic repeat and request (HARQ). Also, the base station transmitsuplink (UL) scheduling information of uplink data to the correspondinguser equipment to notify the corresponding user equipment of time andfrequency domains that can be used by the corresponding user equipment,and information related to encoding, data size, and HARQ. An interfacefor transmitting user traffic or control traffic may be used between thebase stations. A Core Network (CN) may include the AG and a network nodeor the like for user registration of the user equipment. The AG managesmobility of the user equipment on a Tracking Area (TA) basis, whereinone TA includes a plurality of cells.

Although the wireless communication technology developed based on WCDMAhas been evolved into LTE, request and expectation of users andproviders have continued to increase. Also, since another wirelessaccess technology is being continuously developed, new evolution of thewireless communication technology will be required for competitivenessin the future. In this respect, reduction of cost per bit, increase ofavailable service, use of adaptable frequency band, simple structure andopen type interface, proper power consumption of the user equipment,etc. are required.

DISCLOSURE OF THE INVENTION Technical Task

Based on the above discussion, a power measurement method for V2Vcommunication in a wireless communication system and device therefor areprovided.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solutions

To achieve these objects and other advantages, in an aspect of thepresent invention, provided herein is a method of measuring power forvehicle-to-vehicle (V2V) communication by a V2V device in a wirelesscommunication system, including: receiving one or more synchronizationsignals for the V2V communication through a physical sidelink broadcastchannel (PSBCH); and when IDs of the one or more synchronization signalsare interconnected with demodulation reference signal (DMRS) sequencesto which an orthogonal cover code (OCC) with one fixed value is applied,measuring received power of the one or more synchronization signals. Inthis case, the measurement may be performed by averaging for each of theIDs of the one or more synchronization signals.

Additionally, the number of available synchronization signal IDs may begreater than the number of available DMRS sequences.

Additionally, the measurement may be performed except a synchronizationsignal allocated to a symbol adjacent to a DMRS and a synchronizationsignal allocated to a symbol adjacent to a symbol boundary.

Additionally, the PSBCH may further include a measurement field, andcombinations of the measurement field and the DMRS sequences may beconfigured to be mapped to the IDs of the synchronization signals.

Additionally, the DMRS sequences may be comb-type sequences, andcombinations of information indicating whether even mapping or oddmapping is applied to the DMRS sequences and the DMRS sequences may beconfigured to be mapped to the IDs of the synchronization signals.

Additionally, the number of available synchronization signal IDs may belimited to the number of available DMRS sequences.

Additionally, the measurement may be performed when a phase offsetcaused by a frequency error is greater than a predetermined value.

In another aspect of the present invention, provided herein is a methodof receiving a signal for vehicle-to-vehicle (V2V) communication by aV2V device in a wireless communication system, including receiving ademodulation reference signal (DMRS) to which an orthogonal cover code(OCC) with two fixed values is applied for the V2V communication. Whenthe DMRS has three symbols for the V2V communication, the OCC may dependon a predetermined discrete Fourier transform (DFT) matrix.

In a further aspect of the present invention, provided herein is avehicle-to-vehicle (V2V) device for measuring power for V2Vcommunication in a wireless communication system, including: a radiofrequency unit; and a processor. In this case, the processor may beconfigured to: receive one or more synchronization signals for the V2Vcommunication through a physical sidelink broadcast channel (PSBCH); andwhen IDs of the one or more synchronization signals are interconnectedwith demodulation reference signal (DMRS) sequences to which anorthogonal cover code (OCC) with one fixed value is applied, measurereceived power of the one or more synchronization signals. In this case,the measurement may be performed by averaging for each of the IDs of theone or more synchronization signals.

Advantageous Effects

According to the present invention, power measurement for V2Vcommunication can be efficiently performed in a wireless communicationsystem.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved through the present invention are not limited towhat has been particularly described hereinabove and other advantages ofthe present invention will be more clearly understood from the followingdetailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a schematic diagram of an E-UMTS network structure as oneexample of a wireless communication system.

FIG. 2 illustrates structures of control and user planes of a radiointerface protocol between a UE and E-UTRAN based on 3GPP radio accessnetwork standards.

FIG. 3 illustrates physical channels used in the 3GPP LTE system and ageneral signal transmission method using the same.

FIG. 4 illustrates the structure of a radio frame used in the LTEsystem.

FIG. 5 illustrates the resource grid for a downlink slot.

FIG. 6 illustrates the structure of a downlink radio frame used in theLTE system.

FIG. 7 illustrates the structure of an uplink subframe used in the LTEsystem.

FIG. 8 is a reference diagram for explaining D2D (UE-to-UE)communication.

FIG. 9 is a reference diagram for explaining a V2V scenario.

FIG. 10 illustrates the structure of a demodulation reference signal(DMRS) of the LTE system.

FIG. 11 is a reference diagram for explaining the structures of aprimary sidelink synchronization signal (PSSS) and a secondary sidelinksynchronization signal (SSSS) of the LTE system.

FIG. 12 illustrates a base station (BS) and a user equipment (UE)applicable to an embodiment of the present invention.

BEST MODE FOR INVENTION

The following technology may be used for various wireless accesstechnologies such as CDMA (code division multiple access), FDMA(frequency division multiple access), TDMA (time division multipleaccess), OFDMA (orthogonal frequency division multiple access), andSC-FDMA (single carrier frequency division multiple access). The CDMAmay be implemented by the radio technology such as UTRA (universalterrestrial radio access) or CDMA2000. The TDMA may be implemented bythe radio technology such as global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by the radio technologysuch as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, andevolved UTRA (E-UTRA). The UTRA is a part of a universal mobiletelecommunications system (UMTS). A 3rd generation partnership projectlong term evolution (3GPP LTE) is a part of an evolved UMTS (E-UMTS)that uses E-UTRA, and adopts OFDMA in a downlink and SC-FDMA in anuplink. LTE-advanced (LTE-A) is an evolved version of the 3GPP LTE.

For clarification of the description, although the following embodimentswill be described based on the 3GPP LTE/LTE-A, it is to be understoodthat the technical spirits of the present invention are not limited tothe 3GPP LTE/LTE-A. Also, specific terminologies hereinafter used in theembodiments of the present invention are provided to assistunderstanding of the present invention, and various modifications may bemade in the specific terminologies within the range that they do notdepart from technical spirits of the present invention.

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a user equipment andE-UTRAN based on the 3GPP radio access network standard. The controlplane means a passageway where control messages are transmitted, whereinthe control messages are used by the user equipment and the network tomanage call. The user plane means a passageway where data generated inan application layer, for example, voice data or Internet packet dataare transmitted.

A physical layer as the first layer provides an information transferservice to an upper layer using a physical channel. The physical layeris connected to a medium access control (MAC) layer via a transportchannel, wherein the medium access control layer is located above thephysical layer. Data are transferred between the medium access controllayer and the physical layer via the transport channel. Data aretransferred between one physical layer of a transmitting side and theother physical layer of a receiving side via the physical channel. Thephysical channel uses time and frequency as radio resources. In moredetail, the physical channel is modulated in accordance with anorthogonal frequency division multiple access (OFDMA) scheme in adownlink, and is modulated in accordance with a single carrier frequencydivision multiple access (SC-FDMA) scheme in an uplink.

A medium access control (MAC) layer of the second layer provides aservice to a radio link control (RLC) layer above the MAC layer via alogical channel. The RLC layer of the second layer supports reliabledata transmission. The RLC layer may be implemented as a functionalblock inside the MAC layer. In order to effectively transmit data usingIP packets such as IPv4 or IPv6 within a radio interface having a narrowbandwidth, a packet data convergence protocol (PDCP) layer of the secondlayer performs header compression to reduce the size of unnecessarycontrol information.

A radio resource control (RRC) layer located on the lowest part of thethird layer is defined in the control plane only. The RRC layer isassociated with configuration, re-configuration and release of radiobearers (‘RBs’) to be in charge of controlling the logical, transportand physical channels. In this case, the RB means a service provided bythe second layer for the data transfer between the user equipment andthe network. To this end, the RRC layers of the user equipment and thenetwork exchange RRC message with each other. If the RRC layer of theuser equipment is RRC connected with the RRC layer of the network, theuser equipment is in an RRC connected mode. If not so, the userequipment is in an RRC idle mode. A non-access stratum (NAS) layerlocated above the RRC layer performs functions such as sessionmanagement and mobility management.

One cell constituting a base station eNB is set to one of bandwidths of1.4, 3.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to several user equipments. At this time, differentcells may be set to provide different bandwidths.

As downlink transport channels carrying data from the network to theuser equipment, there are provided a broadcast channel (BCH) carryingsystem information, a paging channel (PCH) carrying paging message, anda downlink shared channel (SCH) carrying user traffic or controlmessages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted via the downlink SCH or anadditional downlink multicast channel (MCH). Meanwhile, as uplinktransport channels carrying data from the user equipment to the network,there are provided a random access channel (RACH) carrying an initialcontrol message and an uplink shared channel (UL-SCH) carrying usertraffic or control message. As logical channels located above thetransport channels and mapped with the transport channels, there areprovided a broadcast control channel (BCCH), a paging control channel(PCCH), a common control channel (CCCH), a multicast control channel(MCCH), and a multicast traffic channel (MTCH).

FIG. 3 is a diagram illustrating physical channels used in a 3GPP LTEsystem and a general method for transmitting a signal using the physicalchannels.

The user equipment performs initial cell search such as synchronizingwith the base station when it newly enters a cell or the power is turnedon at step S301. To this end, the user equipment synchronizes with thebase station by receiving a primary synchronization channel (P-SCH) anda secondary synchronization channel (S-SCH) from the base station, andacquires information such as cell ID, etc. Afterwards, the userequipment may acquire broadcast information within the cell by receivinga physical broadcast channel (PBCH) from the base station. Meanwhile,the user equipment may identify a downlink channel status by receiving adownlink reference signal (DL RS) at the initial cell search step.

The user equipment which has finished the initial cell search mayacquire more detailed system information by receiving a physicaldownlink shared channel (PDSCH) in accordance with a physical downlinkcontrol channel (PDCCH) and information carried in the PDCCH at stepS302.

Afterwards, the user equipment may perform a random access procedure(RACH) such as steps S303 to S306 to complete access to the basestation. To this end, the user equipment may transmit a preamble througha physical random access channel (PRACH) (S303), and may receive aresponse message to the preamble through the PDCCH and the PDSCHcorresponding to the PDCCH (S304). In case of a contention based RACH,the user equipment may perform a contention resolution procedure such astransmission (S305) of additional physical random access channel andreception (S306) of the physical downlink control channel and thephysical downlink shared channel corresponding to the physical downlinkcontrol channel.

The user equipment which has performed the aforementioned steps mayreceive the physical downlink control channel (PDCCH)/physical downlinkshared channel (PDSCH) (S307) and transmit a physical uplink sharedchannel (PUSCH) and a physical uplink control channel (PUCCH) (S308), asa general procedure of transmitting uplink/downlink signals. Controlinformation transmitted from the user equipment to the base station willbe referred to as uplink control information (UCI). The UCI includesHARQ ACK/NACK (Hybrid Automatic Repeat and reQuestAcknowledgement/Negative-ACK), SR (Scheduling Request), CSI (ChannelState Information), etc. In this specification, the HARQ ACK/NACK willbe referred to as HARQ-ACK or ACK/NACK (A/N). The HARQ-ACK includes atleast one of positive ACK (simply, referred to as ACK), negative ACK(NACK), DTX and NACK/DTX. The CSI includes CQI (Channel QualityIndicator), PMI (Precoding Matrix Indicator), RI (Rank Indication), etc.Although the UCI is generally transmitted through the PUCCH, it may betransmitted through the PUSCH if control information and traffic datashould be transmitted at the same time. Also, the user equipment maynon-periodically transmit the UCI through the PUSCH in accordance withrequest/command of the network.

FIG. 4 is a diagram illustrating a structure of a radio frame used in anLTE system.

Referring to FIG. 4, in a cellular OFDM radio packet communicationsystem, uplink/downlink data packet transmission is performed in a unitof subframe, wherein one subframe is defined by a given time intervalthat includes a plurality of OFDM symbols. The 3GPP LTE standardsupports a type 1 radio frame structure applicable to frequency divisionduplex (FDD) and a type 2 radio frame structure applicable to timedivision duplex (TDD).

FIG. 4(a) is a diagram illustrating a structure of a type 1 radio frame.The downlink radio frame includes 10 subframes, each of which includestwo slots in a time domain. A time required to transmit one subframewill be referred to as a transmission time interval (TTI). For example,one subframe may have a length of 1 ms, and one slot may have a lengthof 0.5 ms. One slot includes a plurality of OFDM symbols in a timedomain and a plurality of resource blocks (RB) in a frequency domain.Since the 3GPP LTE system uses OFDM in a downlink, OFDM symbolsrepresent one symbol interval. The OFDM symbol may be referred to asSC-FDMA symbol or symbol interval. The resource block (RB) as a resourceallocation unit may include a plurality of continuous subcarriers in oneslot.

The number of OFDM symbols included in one slot may be varied dependingon configuration of a cyclic prefix (CP). Examples of the CP include anextended CP and a normal CP. For example, if the OFDM symbols areconfigured by the normal CP, the number of OFDM symbols included in oneslot may be 7. If the OFDM symbols are configured by the extended CP,since the length of one OFDM symbol is increased, the number of OFDMsymbols included in one slot is smaller than that of OFDM symbols incase of the normal CP. For example, in case of the extended CP, thenumber of OFDM symbols included in one slot may be 6. If a channel stateis unstable like the case where the user equipment moves at high speed,the extended CP may be used to reduce inter-symbol interference.

If the normal CP is used, since one slot includes seven OFDM symbols,one subframe includes 14 OFDM symbols. At this time, first maximum threeOFDM symbols of each subframe may be allocated to a physical downlinkcontrol channel (PDCCH), and the other OFDM symbols may be allocated toa physical downlink shared channel (PDSCH).

FIG. 4(b) is a diagram illustrating a structure of a type 2 radio frame.The type 2 radio frame includes two half frames, each of which includesfour general subframes, which include two slots, and a special subframewhich includes a downlink pilot time slot (DwPTS), a guard period (GP),and an uplink pilot time slot (UpPTS).

In the special subframe, the DwPTS is used for initial cell search,synchronization or channel estimation at the user equipment. The UpPTSis used for channel estimation at the base station and uplinktransmission synchronization of the user equipment. In other words, theDwPTS is used for downlink transmission, whereas the UpPTS is used foruplink transmission. Especially, the UpPTS is used for PRACH preamble orSRS transmission. Also, the guard period is to remove interferenceoccurring in the uplink due to multipath delay of downlink signalsbetween the uplink and the downlink.

Configuration of the special subframe is defined in the current 3GPPstandard document as illustrated in Table 1 below. Table 1 illustratesthe DwPTS and the UpPTS in case of T_(s)=1/(15000×2048), and the otherregion is configured for the guard period.

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal Extended Normal Extended subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 ·T_(s) — — —

In the meantime, the structure of the type 2 radio frame, that is,uplink/downlink configuration (UL/DL configuration) in the TDD system isas illustrated in Table 2 below.

TABLE 2 Uplink- Downlink- downlink to-Uplink configu- Switch-pointSubframe number ration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 msD S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D DD D 6 5 ms D S U U U D S U U D

In the above Table 2, D means the downlink subframe, U means the uplinksubframe, and S means the special subframe. Also, Table 2 alsoillustrates a downlink-uplink switching period in the uplink/downlinksubframe configuration of each system.

The structure of the aforementioned radio frame is only exemplary, andvarious modifications may be made in the number of subframes included inthe radio frame, the number of slots included in the subframe, or thenumber of symbols included in the slot.

FIG. 5 illustrates a resource grid for a downlink slot.

Referring to FIG. 5, a DL slot includes N_(symb) ^(DL) OFDM symbols in atime domain and N_(RB) ^(DL) resource blocks in a frequency domain.Since each of the resource blocks includes N_(SC) ^(RB) subcarriers, theDL slot includes N_(RB) ^(DL)×N_(SC) ^(RB) subcarriers in the frequencydomain. Although FIG. 5 shows an example in which the DL slot includes 7OFDM symbols and the resource block includes 12 subcarriers, the presentinvention is not limited thereto. For instance, the number of OFDMsymbols included in the DL slot can vary depending to a length of acyclic prefix (CP).

Each element on a resource grid is referred to as a resource element(RE) and a single resource element is indicated by one OFDM symbol indexand one subcarrier index. A single RB is configured with N_(symb)^(DL)×N_(SC) ^(RB) resource elements. The number (N_(RB) ^(DL)) ofresource blocks included in the DL slot depends on a DL transmissionbandwidth configured in a cell.

FIG. 6 illustrates a structure of a downlink radio frame.

Referring to FIG. 6, up to 3 (or 4) OFDM symbols located at a head partof a first slot of a subframe correspond to a control region to which acontrol channel is assigned. And, the rest of OFDM symbols correspond toa data region to which PDSCH (physical downlink shared channel) isassigned. For example, DL control channels used in the LTE system mayinclude a PCFICH (physical control format indicator channel), a PDCCH(physical downlink control channel), a PHICH (physical hybrid ARQindicator channel) and the like. The PCFICH is transmitted on a firstOFDM symbol of a subframe and carries information on the number of OFDMsymbols in the subframe used for control channel transmission. The PHICHcarries an HARQ ACK/NACK (hybrid automatic repeat requestacknowledgment/negative-acknowledgment) signal in response to ULtransmission.

Control information transmitted on the PDCCH is called DCI (downlinkcontrol information). The DCI includes resource allocation informationand other control information for a user equipment or a user equipmentgroup. For instance, the DCI may include UL/DL scheduling information,UL transmission (Tx) power control command and the like.

The PDCCH carries transmission format and resource allocationinformation of a DL-SCH (downlink shared channel), transmission formatand resource allocation information of a UL-SCH (uplink shared channel),paging information on a PCH (paging channel), system information on aDL-SCH, resource allocation information of a higher-layer controlmessage such as a random access response transmitted on a PDSCH, a Txpower control command set for individual user equipments in a userequipment group, a Tx power control command, activation indicationinformation of a VoIP (voice over IP) and the like. A plurality ofPDCCHs may be transmitted in a control region. A user equipment canmonitor a plurality of PDCCHs. The PDCCH is transmitted on aggregationof one or more consecutive CCEs (control channel elements). In thiscase, the CCE is a logical assignment unit used in providing the PDCCHwith a coding rate based on a radio channel state. The CCE correspondsto a plurality of REGs (resource element groups). The PDCCH format andthe number of PDCCH bits are determined depending on the number of CCEs.A base station determines the PDCCH format in accordance with DCI to betransmitted to a user equipment and attaches CRC (cyclic redundancycheck) to control information. The CRC is masked with an identifier(e.g., RNTI (radio network temporary identifier)) in accordance with anowner or a purpose of use. For instance, if a PDCCH is provided for aspecific user equipment, CRC may be masked with an identifier (e.g.,C-RNTI (cell-RNTI)) of the corresponding user equipment. If a PDCCH isprovided for a paging message, CRC may be masked with a pagingidentifier (e.g., P-RNTI (paging-RNTI)). If a PDCCH is provided forsystem information (particularly, SIC (system information block)), CRCmay be masked with an SI-RNTI (system information-RNTI). In addition, ifa PDCCH is provided for a random access response, CRC may be masked withan RA-RNTI (random access-RNTI).

FIG. 7 illustrates a structure of an uplink subframe used in an LTEsystem.

Referring to FIG. 7, an uplink subframe includes a plurality (e.g., 2slots) of slots. Each of the slots may include a different number ofSC-FDMA symbols depending on a length of CP. The UL subframe may bedivided into a data region and a control region in the frequency domain.The data region includes a PUSCH and is used to transmit such a datasignal as audio and the like. The control region includes a PUCCH and isused to transmit UCI (uplink control information). The PUCCH includes anRB pair located at both ends of the data region on a frequency axis andis hopped on a slot boundary.

The PUCCH can be used to transmit the following control information.

-   -   SR (scheduling request): This is information used to request a        UL-SCH resource and is transmitted using an OOK (on-off keying)        scheme.    -   HARQ ACK/NACK: This is a response signal in response to a DL        data packet on a PDSCH and indicates whether the DL data packet        has been successfully received. 1-bit ACK/NACK is transmitted as        a response to a single downlink codeword and 2-bit ACK/NACK is        transmitted as a response to two downlink codewords.    -   CSI (channel state information): This is feedback information on        a downlink channel. The CSI includes a channel quality indicator        (CQI). MIMO (multiple input multiple output) related feedback        information includes a rank indicator (RI), a precoding matrix        indicator (PMI), a precoding type indicator (PTI) and the like.        20-bit is used in each subframe.

The amount of control information (UCI) that a user equipment cantransmit in a subframe depends on the number of SC-FDMA symbolsavailable for transmission of the control information. The SC-FDMAsymbols available for the transmission of the control informationcorrespond to the rest of SC-FDMA symbols except SC-FDMA symbols usedfor transmitting a reference signal in the subframe. In case of asubframe in which a sounding reference signal (SRS) is configured, thelast SC-FDMA symbol of the subframe is excluded from the SC-FDMA symbolsavailable for the transmission of the control information. The referencesignal is used for coherent detection of a PUCCH.

Hereinafter, D2D (UE-to-UE) communication will be described.

A D2D communication scheme can be mainly classified as a schemesupported by a network/coordination station (e.g., base station) and ascheme not supported by the network/coordination station.

Referring to FIG. 8, FIG. 8 (a) illustrates a scheme in which thenetwork/coordination station intervenes in transmission and reception ofcontrol signals (e.g., grant message), HARQ, channel state information,etc. and user equipments that perform D2D communication transmit andreceive data only. On the other hand, FIG. 8 (b) illustrates a scheme inwhich the network provides minimum information (e.g., D2D connectioninformation available in a corresponding cell) only but the userequipments that perform D2D communication establish links to transmitand receive data.

FIG. 9 is a diagram illustrating a V2X (vehicle to everything)communication environment.

If a vehicle accident occurs, many lives are lost, and serious propertydamage is caused. Thus, the demand for a technology capable of securingsafety of pedestrians as well as safety of people in a vehicle has beenincreased. In addition, a technology based on hardware and softwarededicated to the vehicle has been grafted onto the vehicle.

Recently, the LTE-based V2X (vehicle-to-everything) communicationtechnology, which has been evolved from 3GPP, reflects the tendency inwhich the information technology (IT) is grafted onto the vehicle. Aconnectivity function is applied to some kinds of vehicles, and effortsare continuously made to research and develop vehicle-to-vehicle (V2V)communication, vehicle-to-infrastructure (V2I) communication,vehicle-to-pedestrian (V2P) communication, and vehicle-to-network (V2N)communication with the evolution of communication functions.

According to V2X communication, a vehicle consistently broadcastsinformation on its own locations, speeds, directions, etc. Afterreceiving the broadcasted information, a nearby vehicle utilizes theinformation for accident prevention by recognizing movements of otheradjacent vehicles.

That is, in a similar manner that an individual person carries a userequipment such as a smartphone, a smartwatch or the like, a specifictype of user equipment (UE) can be installed in each vehicle. Here, a UEinstalled in a vehicle means a device that actually receivescommunication services from a communication network. For example, the UEinstalled in the vehicle can be accessed to an eNB in E-UTRAN andprovided with communication services.

However, there are various items that should be considered for a processfor implementing V2X communication in a vehicle. This is becauseastronomical costs are required for the installation of traffic safetyfacilities such as a V2X base station and the like. That is, to supportV2X communication on all roads where the vehicle can move, it isnecessary to install hundreds or thousands of V2X base stations or more.Moreover, since each network node accesses the Internet or a centralizedcontrol server using a wired network basically for stable communicationwith a server, installation and maintenance costs for the wired networkare also high.

Hereinafter, a signal to which an orthogonal cover code (OCC) forcompensating for a frequency offset error in a V2V scenario is appliedwill be described. Although the present invention is described based onthe V2V scenario for convenience of description, the invention can alsobe applied to other scenarios including a D2D scenario, etc.

In V2X communication, the subframe structure designed for theconventional LTE physical uplink shared channel (PUSCH) can be used.FIG. 10a shows a DMRS structure in a subframe with the normal CP of thecurrent LTE system, and FIG. 10b shows a DMRS structure in a subframewith an extended CP of the current LTE system. Basically, according tothe DMRS design shown in FIG. 10a or FIG. 10b , a DMRS is designed suchthat it is mapped to all resource elements of several OFDM symbols in asubframe in consideration of a peak-to-average power ratio (PAPR). InV2V communication, a receiver can be installed in a vehicle with theadvance of the technology. Hence, the PARR may not cause any seriousproblem. Thus, the present invention concentrates on DMRS designconsidering a frequency offset rather than the PARR.

In the V2V scenario currently discussed in the LTE system, 5.9 GHz,which is used for dedicated short range communication (DSRC), can alsobe considered as a center frequency target.

Currently, the requirement of an initial frequency offset is 10 ppm(pulses per minute), and the requirement of a residual frequency offsetis +/−0.1 ppm. Assuming that two vehicles are synchronized with eachother based on a signal provided by a common eNB, a common vehicle, oranother common source, a frequency offset difference between the twovehicles may be +/−0.2 ppm. If a vehicle establishes synchronizationwith a different vehicle which has established synchronization, it mightsay that the vehicle has two-hop synchronization. In this case, if twovehicles establish synchronization through the different vehicle, thetwo vehicles have two-hop synchronization, and a frequency offsetdifference therebetween may be +/−0.4 ppm. If two vehicles establishthree-hop synchronization through the same vehicle, a frequency offsetdifference therebetween may be +/−0.6 ppm.

Assuming that a DMRS is designed as shown in FIG. 10a and the twocolumns of DMRS are used to compensate for a frequency offset, it isnecessary to measure the amount of a phase offset due to increase in thefrequency offset during 0.5 ms. This is because the frequency offset canbe estimated based on the amount of the phase offset.

Table 3 below shows the amount of increase in a phase offset during 0.5ms depending on the center frequency or multi-hop synchronization.

TABLE 3 Phase increment over 0.5 ms (DMRS interval) Carrier Frequency0.1 ppm 0.4 ppm 0.6 ppm 700 MHz  70 Hz => 280 Hz =>  420 Hz => 0.22 rad0.88 rad 1.32 rad 2 GHz 200 Hz => 800 Hz => 1200 Hz => 0.63 rad 2.51 rad3.77 rad > pi 5.9 GHz 590 Hz => 1.85 rad

Referring to Table 3, at the center frequency of 700 MHz, even thoughthe frequency offset is +/−0.6 ppm, the increase in the phase offsetdoes not exceed the value of pi (π). Thus, at the center frequency of700 MHz, the current DMRS structure can be used in adjusting thefrequency offset. However, when the center frequency increases to 2 GHzwhile the same frequency offset of +/−0.6 ppm is maintained, the phaseoffset value exceeds the value of pi. Hence, a problem may occur incompensating for the frequency offset using the current DMRS structure.Moreover, at the center frequency of 5.9 GHz, even when the frequencyoffset is only +/−0.2 ppm, the phase offset value exceeds the value ofpi. Hence, it is difficult to compensate the frequency offset valueusing the current DMRS structure.

In fact, the frequency offset of +/−0.2 ppm may correspond to theminimum frequency offset value in V2V. That is, when two vehicles aresynchronized with respect to a single vehicle or an eNB, the twovehicles should assume that the minimum frequency offset is equal to orgreater than +/−0.2 ppm in order to communicate with each other. In thiscase, if the center frequency is 5.9 GHz, it is difficult to compensatefor the frequency offset using the current DMRS structure.

The simulation results in Table 4 shows the amount of the phase offsetwhen it is assumed that the frequency offset is x ppm and the DMRS ismapped to at an interval of y symbols.

It can be seen from Table 4 that in the case of the frequency offset of+/−0.2 ppm, the DMRS needs to be mapped at an interval of five symbols.In the case of the frequency offset of +/−0.4 ppm, the DMRS needs to bemapped at an interval of two symbols. When the frequency offset is equalto or greater than +/−0.6 ppm, the DMRS should be mapped at an intervalof one symbol to compensate for the frequency offset.

TABLE 4 0.1 ppm 0.2 ppm 0.3 ppm 0.4 ppm 0.5 ppm 0.6 ppm 0.7 ppm 0.8 ppm0.9 ppm 1.0 ppm 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1symbol 0.07142860.264791 0.529583 0.794374 1.059165 1.323957 1.588748 1.853539 2.1183312.383122 2.647913 2symbol 0.1428571 0.529583 1.059165 1.588748 2.1183312.647913 3.1775 3.70708 4.23666 4.76624 5.29583 3symbol 0.21428570.794374 1.588748 2.383122 3.1775 3.97187 4.76624 5.56062 6.354997.14937 7.94374 4symbol 0.2857143 1.059165 2.118331 3.1775 4.236665.29583 6.35499 7.41416 8.47332 9.53249 10.5917 5symbol 0.35714291.323957 2.647913 3.97187 5.29583 6.61978 7.94374 9.2677 10.5917 11.915613.2396 6symbol 0.4285714 1.588748 3.1775 4.76624 6.35499 7.943749.53249 11.1212 12.71 14.2987 15.8875 7symbol 0.5 1.853539 3.707085.56062 7.41416 9.2677 11.1212 12.9748 14.8283 16.6819 18.5354 8symbol0.5714286 2.118331 4.23666 6.35499 8.47332 10.5917 12.71 14.8283 16.946619.065 21.1833 9symbol 0.6428571 2.383122 4.76624 7.14937 9.5324911.9156 14.2987 16.6819 19.065 21.4481 23.8312 10symbol  0.71428572.647913 5.29583 7.94374 10.5917 13.2396 15.8875 18.5354 21.1833 23.831226.4791 11symbol  0.7857143 2.912705 5.82541 8.73811 11.6508 14.563517.4762 20.3889 23.3016 26.2143 29.127 12symbol  0.8571429 3.17756.35499 9.53249 12.71 15.8875 19.065 22.2425 25.42 28.5975 31.77513symbol  0.9285714 3.44229 6.88457 10.3269 13.7691 17.2114 20.653724.096 27.5383 30.9806 34.4229 14symbol  1 3.70708 7.41416 11.121214.8283 18.5354 22.2425 25.9495 29.6566 33.3637 37.0708

The DMRS design with an interval of seven OFDM symbols, which is usedfor UL transmission in the current LTE system, is not suitable for thesystem with a large frequency offset. That is, it is possible to supportthe frequency offset adjustment by reducing the OFDM symbol intervalbetween DMRSs.

Meanwhile, an orthogonal cover code (OCC) has been used for the currentuplink DMRS. Since the DMRS is mapped to two OFDM symbols, code [1 1]and code [1 −1] are used as the current OCC.

However, considering the frequency offset and Doppler effect, areceiving UE may be unable to segment the OCC. When two OFDM symbols areused for DMRSs, if a phase change caused by an offset during the timeinterval from a DMRS to a next neighboring DMRS is greater than π, thereceiving UE cannot clearly understand the phase change. For example, ifthe phase change is 190 degrees, the receiving UE may not determinewhether the phase change is 190 or 170 degrees. However, if codes [1 1]and [1 −1] are used, the UE should segment a signal into two codes: acode where the difference of π is reflected and a code where thedifference of π is not reflected, during the time interval from the DMRSto the next neighboring DMRS. To this end, the phase change due to theoffset should be less than π/2. However, when a UE moving at high speedas in V2X communication is set as a target, the phase change caused bythe Doppler effect and frequency offset may significantly increase, andthus the OCC may not operate correctly.

Accordingly, in this case, one OCC with a fixed value should be usedinstead of a plurality of OCCs.

If one code with a fixed value is used as the OCC, the number of DMRSsequences is reduced by half. In addition, in the case of a channelcarrying a PSSS and an SSSS such as a physical sidelink broadcastchannel (PSBCH), a synchronization signal ID is interconnected with aDMRS sequence. Thus, a receiving UE can obtain the synchronizationsignal ID by performing blind detection of the DMRS sequence. However,as described above, in the case of using the OCC with the fixed value,the number of DMRS sequences is reduced by half, and thus it may besmaller than the number of synchronization signal IDs. Currently, sincetwo root indices are used for the PSSS of the PSBCH and 168 IDs are usedfor the SSSS, the total number of available IDs of synchronizationsignals becomes 336. In addition, considering that 30 base sequences, 8CSs and 2 OCCs are used for DMRS sequences for the PSBCH, it can be seenthat there is a total of 480 sequences. However, in this case, since thenumber of available sequences is reduced as 240 due to use of the OCCwith the fixed value, all the synchronization signal IDs cannot beaccommodated.

Accordingly, the present invention proposes first to eighth methods toovercome the insufficient number of DMRS sequences to be matched withsynchronization signal IDs.

First Method

As the first method of the present invention, provided is a method fordirectly measuring received power of a synchronization signal (e.g.,PSSS and/or SSSS) in a V2X communication scenario. For this measurement,averaging or filtering is performed per ID of a detected PSSS or SSSS.

According to D2D communication defined in Release 12/13 in the LTEsystem, a PSBCH DMRS has been used for synchronization signalmeasurement, particularly to measure signals used by D2D communicationUEs only. If it is assumed that all UEs can use a PSBCH in V2Xcommunication, it is possible to directly measure a synchronizationsignal as in the first method. Exceptionally, in this case, power of asynchronization signal adjacent to the DMRS or power of asynchronization signal transmitted in the symbol adjacent to a subframeboundary may not be measured. This is because since inter-cellinterference (ICI) may occur due to a power amplifier transient, it ispreferable to exclude the corresponding symbol from the measurement.

Second Method

The above-described first method has a disadvantage in that the newmeasurement should be introduced. Hence, to maintain a method ofmeasuring a PSBCH DMRS as in the conventional sidelink-reference signalreceived power (S-RSRP) measurement, a method of separating measurementwhen SLSSs (PSSS/SSSS) have different IDs in spite of the same DMRS isprovided as the second method. For example, when SLSS IDs are differentfrom each other in spite of the same DMRS, it is proposed not to performaveraging/filtering together.

That is, in case an OCC cannot be used due to a high frequency offset,DMRSs may not be distinguished from each other by the OCC, and the DMRSsmay be identical to each other even though SLSS IDs are different. Inthis case, if DMRS measurement averaging/filtering is performed onidentical SLSS IDs only, it is possible to prevent erroneous S-RSRPresults due to synthesized measurement.

Third Method

According to the third method of the present invention, 12 cyclic shiftsare used to map a DMRS sequence to a synchronization signal ID.Specifically, among the 12 cyclic shifts, only 8 cyclic shifts areselected and used in the LTE system, whereas all of the 12 cyclic shiftscan be used in the V2X scenario.

Fourth Method

According to the fourth method of the present invention, an N-bitmeasurement field (where N is a natural number) is added to a PSBCH, andcombination of the measurement field and DMRS sequences are mapped tosynchronization signal IDs. Here, N may be 1. For example, when an OCCcannot be used, one bit where IDs are distinguished by the OCC may beincluded in the PSBCH. By doing so, a UE may perform measurementaveraging only when measurement fields are the same.

Fifth Method

According to the fifth method of the present invention, an OCC (code [11] and code [1 −1]) is applied to a PSSS and/or SSSS, and combinationsof the OCC applied to sidelink synchronization signals and DMRSsequences are mapped to synchronization signal IDs.

FIG. 11A shows the PSBCH structure of the LTE system in the case of thenormal CP, and FIG. 11B shows the PSBCH structure in the case of theextended CP. In FIGS. 11A and 11B, each of the PSSS and SSSS is mappedto two symbols, and code [1 1] or [1 −1] may be applied to the twosymbols. That is, a synchronization signal where the OCC is applied iscombined with a DMRS sequence, and then the combination can be mapped toa synchronization signal ID.

Sixth Method

According to the sixth method of the present invention, when a comb typeof sequence is used for a DMRS, combinations of information indicatingwhether even mapping or odd mapping is applied and DMRS sequences aremapped to synchronization signal IDs. When the even mapping is used, itis observed that the same half-length OFDM symbol is repeated in thetime domain. On the other hand, when the odd mapping is used, it isobserved that a second block of the half-length OFDM symbol has anegative sign in the time domain, i.e., its sign is inverted. That is,by comparing the observation results, a receiving UE can identifymeasurement.

Seventh Method

According to the seventh method of the present invention, both an SSSfor subframe 0 (i.e., SFN #0) and an SSS for subframe 5 (i.e., SFN #5)are used to generate an SSSS, and combinations of information indicatingwhether subframe 0 or subframe 5 is used and DMRS sequences are mappedto synchronization signal IDs (in this case, an OCC may not be used).

Currently, an SSSS for subframe 0 is used in D2D communication. However,if an SSSS for subframe 5 is used together with the SSSS for subframe 0,1 bit of information can be further generated. That is, the generated1-bit information is combined with a DMRS sequence, and then thecombination can be mapped to a synchronization signal ID.

Eighth Method

According to the eighth method of the present invention, asynchronization signal (PSSS and/or SSSS) can be used to identify asynchronization signal ID, and a DMRS can be used for measurement.

Further, according to the present invention, it is possible to use anSSS for subframe 5 in V2X communication in order to indicate that it isfor global navigation satellite system (GNSS) synchronization or globalpositioning system (GPS) synchronization.

Alternatively, when the number of DMRS sequences is smaller than thenumber of synchronization signal IDs (synchronization IDs), it ispossible to restrict the number of synchronization IDs below the numberof DMRS sequences in order to measure synchronization through a DMRS. Inother words, an eNB may set the number of IDs to be used for sidelinksynchronization with reference to the number of available DMRSs and theninform UEs of this fact to prevent the UEs from performing unnecessarysynchronization signal search. By doing so, even when the number of DMRSsequences is reduced, it is possible to achieve stable S-RSPRmeasurement.

When the method for sidelink synchronization measurement or method forchanging SLSS/PSBCH formats proposed in the present invention is used,which one of the aforementioned methods (including the synchronizationmeasurement method used in Re1.13 D2D) will be used could be determinedin advance. For example, at a high frequency of 6 GHz, an OCC is notused because a phase offset caused by a frequency offset is large, andthus the number of DMRS sequences becomes insufficient. Accordingly, oneof the aforementioned methods can be applied. Meanwhile, at a lowfrequency of 2 GHz, an OCC is used because a phase offset caused by afrequency offset is relatively small, and thus the number of DMRSsequences becomes greater than that of synchronization IDs. Thus, thesynchronization measurement method used in Re1.13 D2D can be applied.

Alternatively, a network can inform UEs which one of the newsynchronization measurement method (including the synchronizationmeasurement method used in Re1.13 D2D) and method for changingSLSS/PSBCH formats will be used, through higher layer signaling (e.g.,RRC or SIB).

To handle a case where a UE is out of network coverage, how the sidelinksynchronization measurement should be performed or how an SLSS/PSBCHshould be transmitted and measured may be determined in advance. Forexample, when a UE connected to the network is detached from thenetwork, how the UE should perform the synchronization measurement canbe informed the UE in advance through preconfiguration signaling.

Alternatively, an OCC may have two values instead of a fixed value.Table 5 shows the current PSBCH DMRS sequences, and in this case, threePSBCH DMRS symbols may be considered.

TABLE 5 Parameter in clause 5.5.2.1 PSBCH Group hopping disabled ƒ_(ss)└N_(ID) ^(SL)/16┘mod 30 Sequence hopping disabled Cyclic shift n_(cs, λ)└N_(ID) ^(SL)/2┘mod 8 Orthogonal sequence └w^(λ)(0) w^(λ)(1)┘ [+1 +1] ifN_(ID) ^(SL) mod 2 = 0 [+1 −1] if N_(ID) ^(SL) mod 2 = 1 Referencesignal length M_(sc) ^(RS) M_(sc) ^(PSBCH) Number of layers υ 1 Numberof antenna ports P 1

In this case, using a discrete Fourier transform (DFT) matrix, the OCCfor three DMRSs can be defined as follows.

${\left\lbrack {1\mspace{14mu} 1\mspace{14mu} 1} \right\rbrack \left\lbrack {1\mspace{14mu} e^{j\frac{2\pi}{3}}e^{j\frac{4\pi}{3}}} \right\rbrack}\left\lbrack {1\mspace{14mu} e^{j\frac{4\pi}{3}}e^{j\frac{8\pi}{3}}} \right\rbrack$

However, if all the above vectors are used, the CS, OCC, and basesequence in Table 5 should be modified by considering the vectors. Tofacilitate the implementation of the UE while maintaining thecompatibility, only two among the three DFT vectors may be used for theOCC.

For example, the following two vectors may be used for the OCC.

$\left\lbrack {1\mspace{14mu} 1\mspace{14mu} 1} \right\rbrack \left\lbrack {1\mspace{14mu} e^{j\frac{2\pi}{3}}e^{j\frac{4\pi}{3}}} \right\rbrack$

As another example, the following two vectors may be used for the OCC.

$\left\lbrack {1\mspace{14mu} 1\mspace{14mu} 1} \right\rbrack \left\lbrack {1\mspace{14mu} e^{j\frac{4\pi}{3}}e^{j\frac{8\pi}{3}}} \right\rbrack$

As a further example, the following two vectors may be used for the OCC.

$\left\lbrack {1\mspace{14mu} e^{j\frac{2\pi}{3}}e^{j\frac{4\pi}{3}}} \right\rbrack \left\lbrack {1\mspace{14mu} e^{j\frac{4\pi}{3}}e^{j\frac{8\pi}{3}}} \right\rbrack$

FIG. 12 illustrates a base station (BS) and a user equipment (UE)applicable to an embodiment of the present invention.

If a relay node is included in a wireless communication system,communication in a backhaul link is performed between the BS and therelay node and communication in an access link is performed between therelay node and the UE. Therefore, the BS or UE shown in the drawing canbe substituted with the relay node in some cases.

Referring to FIG. 12, a wireless communication system includes a basestation (BS) 110 and a user equipment (UE) 120. The base station 110includes a processor 112, a memory 114 and an RF (radio frequency) unit116. The processor 112 can be configured to implement the proceduresand/or methods proposed in the present invention. The memory 114 isconnected to the processor 112 and stores various kinds of informationrelated to operations of the processor 112. The RF unit 116 is connectedto the processor 112 and transmits and/or receives radio or wirelesssignals. The user equipment 120 includes a processor 122, a memory 124and an RF unit 126. The processor 122 can be configured to implement theprocedures and/or methods proposed in the present invention. The memory124 is connected to the processor 122 and stores various kinds ofinformation related to operations of the processor 122. The RF unit 126is connected to the processor 122 and transmits and/or receives radio orwireless signals. The base station 110 and/or the user equipment 120 canhave a single antenna or multiple antennas.

The above-described embodiments may correspond to combinations ofelements and features of the present invention in prescribed forms. And,it may be able to consider that the respective elements or features maybe selective unless they are explicitly mentioned. Each of the elementsor features may be implemented in a form failing to be combined withother elements or features. Moreover, it may be able to implement anembodiment of the present invention by combining elements and/orfeatures together in part. A sequence of operations explained for eachembodiment of the present invention may be modified. Some configurationsor features of one embodiment may be included in another embodiment orcan be substituted for corresponding configurations or features ofanother embodiment. And, it is apparently understandable that a newembodiment may be configured by combining claims failing to haverelation of explicit citation in the appended claims together or may beincluded as new claims by amendment after filing an application.

In this disclosure, a specific operation explained as performed by abase station can be performed by an upper node of the base station insome cases. In particular, in a network constructed with a plurality ofnetwork nodes including a base station, it is apparent that variousoperations performed for communication with a user equipment can beperformed by a base station or other network nodes except the basestation. In this case, ‘base station’ can be replaced by such aterminology as a fixed station, a Node B, an eNodeB (eNB), an accesspoint and the like.

The embodiments of the present invention may be implemented usingvarious means. For instance, the embodiments of the present inventionmay be implemented using hardware, firmware, software and/or anycombinations thereof. In case of the implementation by hardware, oneembodiment of the present invention may be implemented by at least oneof ASICs (application specific integrated circuits), DSPs (digitalsignal processors), DSPDs (digital signal processing devices), PLDs(programmable logic devices), FPGAs (field programmable gate arrays),processor, controller, microcontroller, microprocessor and the like.

In case of the implementation by firmware or software, one embodiment ofthe present invention may be implemented by modules, procedures, and/orfunctions for performing the above-explained functions or operations.Software code may be stored in a memory unit and may be then driven by aprocessor.

The memory unit may be provided within or outside the processor toexchange data with the processor through the various means known to thepublic.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

INDUSTRIAL APPLICABILITY

The method of measuring power for V2V communication in a wirelesscommunication system and device for the same can be applied to variouswireless communication systems.

What is claimed is:
 1. A method of measuring power forvehicle-to-vehicle (V2V) communication by a V2V device in a wirelesscommunication system, the method comprising: receiving one or moresynchronization signals for the V2V communication through a physicalsidelink broadcast channel (PSBCH); and when IDs of the one or moresynchronization signals are interconnected with demodulation referencesignal (DMRS) sequences to which an orthogonal cover code (OCC) with onefixed value is applied, measuring received power of the one or moresynchronization signals, wherein the measurement is performed byaveraging for each of the IDs of the one or more synchronizationsignals.
 2. The method of claim 1, wherein the number of the IDs of theone or more synchronization signals is greater than the number of theDMRS sequences.
 3. The method of claim 1, wherein the measurement isperformed except a synchronization signal allocated to a symbol adjacentto a DMRS and a synchronization signal allocated to a symbol adjacent toa symbol boundary.
 4. The method of claim 1, wherein the PSBCH furtherincludes a measurement field, and wherein combinations of themeasurement field and the DMRS sequences are configured to be mapped tothe IDs of the synchronization signals.
 5. The method of claim 1,wherein the DMRS sequences are comb-type sequences, and whereincombinations of information indicating whether even mapping or oddmapping is applied to the DMRS sequences and the DMRS sequences areconfigured to be mapped to the IDs of the synchronization signals. 6.The method of claim 1, wherein the number of available synchronizationsignal IDs is limited to the number of available DMRS sequences.
 7. Themethod of claim 1, wherein the measurement is performed when a phaseoffset caused by a frequency error is greater than a predeterminedvalue.
 8. A method of receiving a signal for vehicle-to-vehicle (V2V)communication by a V2V device in a wireless communication system, themethod comprising receiving a demodulation reference signal (DMRS) towhich an orthogonal cover code (OCC) with two fixed values is appliedfor the V2V communication, wherein when the DMRS has three symbols forthe V2V communication, the OCC depends on a predetermined discreteFourier transform (DFT) matrix.
 9. The method of claim 8, wherein theDFT matrix is determined according to the following vectors:${\left\lbrack {1\mspace{14mu} 1\mspace{14mu} 1} \right\rbrack \left\lbrack {1\mspace{14mu} e^{j\frac{2\pi}{3}}e^{j\frac{4\pi}{3}}} \right\rbrack}.$10. The method of claim 8, wherein the DFT matrix is determinedaccording to the following vectors:${\left\lbrack {1\mspace{14mu} 1\mspace{14mu} 1} \right\rbrack \left\lbrack {1\mspace{14mu} e^{j\frac{4\pi}{3}}e^{j\frac{8\pi}{3}}} \right\rbrack}.$11. The method of claim 8, wherein the DFT matrix is determinedaccording to the following vectors:${\left\lbrack {1\mspace{14mu} e^{j\frac{2\pi}{3}}e^{j\frac{4\pi}{3}}} \right\rbrack \left\lbrack {1\mspace{14mu} e^{j\frac{4\pi}{3}}e^{j\frac{8\pi}{3}}} \right\rbrack}.$12. A vehicle-to-vehicle (V2V) device for measuring power for V2Vcommunication in a wireless communication system, the V2V devicecomprising: a radio frequency unit; and a processor wherein theprocessor is configured to: receive one or more synchronization signalsfor the V2V communication through a physical sidelink broadcast channel(PSBCH); and when IDs of the one or more synchronization signals areinterconnected with demodulation reference signal (DMRS) sequences towhich an orthogonal cover code (OCC) with one fixed value is applied,measure received power of the one or more synchronization signals,wherein the measurement is performed by averaging for each of the IDs ofthe one or more synchronization signals.